The catalytic cracking, catalytic pyrolysis and catalytic cracking technology is adopted as the core oil refining technology; catalytic cracking is divided into wax oil catalytic cracking and resid fluid catalytic cracking; reformate produced by the catalytic cracking technology is collectively called catalytic hydrocarbon; obtained catalytic hydrocarbon can be generally fractionated in a fractionating tower to obtain dry gas, liquefied gas, gasoline, diesel oil, heavy oil and other products, wherein the gasoline and the diesel oil accounts for above 70 percent of total gasoline and diesel oil supply amount.
Along with more and more stringent environmental requirements and increasingly improved requirements for the gasoline and the diesel oil, the prior processing method of fractionating the prior catalytic hydrocarbon in the fractionating tower has the following disadvantages that firstly, the quality of the gasoline and the diesel oil produced by adopting the processing method is required to be improved, the gasoline has higher olefin content and lower octane number (RON), the diesel oil has lower cetane number, and the invariability does not satisfy the requirements; secondly, the gasoline with different grades can not be simultaneously produced by adopting the processing method, and the varieties of products are single; and thirdly, the proportion of the produced diesel oil and the gasoline and the demand in the market are not matched, the diesel oil can not satisfy the demands, and the gasoline is beyond the requirements.
In order solve the above problems, a Chinese patent, namely a catalytic hydrocarbon recombination processing method with a Chinese patent number of 03148181.7 is provided; and the Chinese Patents with the patent numbers of 200310103541.9 and 200310103540.4 are improved, which relate to a washing system and a solvent recovery system. However, the problem of how to reduce sulphur and olefin is not related in the disclosed patents.
At present, the sulphur content, the olefin content and the benzene content respectively are not more than 0.05 percent (wt), 35 percent (v) and 2.5 percent (v) upon request of the GB 17930 Gasoline Standard; and most of refineries can satisfy the gasoline quality. However, the sulphur content, the olefin content and the benzene content respectively are not more than 0.015 percent (wt), 30 percent (v) and 1 percent (v) upon request of the State III Gasoline Standard to be executed in 2010. Most of refineries must face to the higher requirements regulated in the State IV Gasoline Standard that the sulphur content and the olefin content respectively are not more than 0.005 percent (wt) and 25 percent (v). The transition from the State III Gasoline Standard to the State IV Gasoline Standard must be considered in the gasoline quality solution, and the better planning scheme is a one-off planning scheme prepared according to the State IV Gasoline Standard.
Due to long-standing status that large proportion difference of gasoline components exists between China and developed country, catalytic cracked gasoline accounts for higher proportion, and reformate and alkylation gasoline account for smaller proportion, the problem of sulphur and olefin reduction required to be solved in the upgrade of gasoline quality mainly is mainly related to the problem of catalytic gasoline.
It is generally acknowledged that 5-10 percent of total sulphur in the catalytic cracking feedstock enters gasoline fraction. According to the characteristics of small catalytic feedstock hydrogenation refining capacity and larger secondary catalytic cracking capacity in domestic refineries as well as residuum coking, the content of sulphur contained in the catalytic gasoline produced by refineries for processing low-sulphur (with 0.3 percent of sulphur content) crude oil is about 200 ppm, the crude oil with 0.8 percent of sulphur content is processed, and the content of sulphur contained in the catalytic gasoline is 900 ppm. Therefore, the difficulty of updating gasoline quality is a problem of transition from olefin reduction to sulphur reduction. The catalytic cracked process or the improvement of catalysts can not basically solve the sulphur problem; the catalytic cracking feed hydrogen desulphurization can not be extensively applied due to large investment, high running expense, limited conditions in the refineries and can not be applicable to the refineries with lower processing capacity. Meanwhile, a catalytic cracking unit is adopted for reducing olefin in a transition manner, thereby increasing the loss of light products and gasoline octane number (RON).
The caustic washing desulphurization is not applicable to deolefination, which also can cause environmental pollution; and the energy consumption high, and the expenses also are higher through hydrotreating the light gasoline.
Therefore, the invention provides a treatment system and a method thereof, which has low cost and low energy consumption and can prepare blended gasoline with low sulphur content, low olefin content and high octane number (RON) under the condition of no pollution so as to solve the difficulties desiderated to be solved in the technical field.